1. Field of the Invention
Generally, the present disclosure relates to the manufacture of semiconductor devices, and, more specifically, to various methods of forming alternative channel semiconductor materials on a non-planar semiconductor device and the resulting device structures.
2. Description of the Related Art
The fabrication of advanced integrated circuits, such as CPU's, storage devices, ASIC's (application specific integrated circuits) and the like, requires the formation of a large number of circuit elements in a given chip area according to a specified circuit layout, wherein so-called metal oxide field effect transistors (MOSFETs or FETs) represent one important type of circuit element that substantially determines performance of the integrated circuits. A conventional FET is a planar device that typically includes a source region, a drain region, a channel region that is positioned between the source region and the drain region, and a gate electrode positioned above the channel region. Current flow through the FET is controlled by controlling the voltage applied to the gate electrode. For example, for an NMOS device, if there is no voltage applied to the gate electrode, then there is no current flow through the NMOS device (ignoring undesirable leakage currents, which are relatively small). However, when an appropriate positive voltage is applied to the gate electrode, the channel region of the NMOS device becomes conductive, and electrical current is permitted to flow between the source region and the drain region through the conductive channel region.
To improve the operating speed of FETs, and to increase the density of FETs on an integrated circuit device, device designers have greatly reduced the physical size of FETs over the past decades. More specifically, the channel length of FETs has been significantly decreased, which has resulted in improving the switching speed and in lowering operation currents and voltages of FETs. However, decreasing the channel length of a FET also decreases the distance between the source region and the drain region. In some cases, this decrease in the separation between the source and the drain makes it difficult to efficiently inhibit the electrical potential of the source region and the channel from being adversely affected by the electrical potential of the drain. This is sometimes referred to as a so-called short channel effect, wherein the characteristic of the FET as an active switch is degraded.
In contrast to a FET, which has a planar structure, a so-called FinFET device has a three-dimensional (3D) structure. FIG. 1A is a perspective view of an illustrative prior art FinFET semiconductor device 10 that is formed above a semiconductor substrate 12 that will be referenced so as to explain, at a very high level, some basic features of a FinFET device 10. In this example, the FinFET device 10 includes three illustrative fins 14, a gate structure 16, sidewall spacers 18 and a gate cap layer 20. The gate structure 16 is typically comprised of a layer of gate insulating material (not separately shown), e.g., a layer of high-k insulating material or silicon dioxide, and one or more conductive material layers (e.g., metal and/or polysilicon) that serve as the gate electrode for the device 10. The fins 14 have a three dimensional configuration: a height 14H, a width 14W and a long-axis or axial length 14L. The axial length 14L corresponds to the direction of current travel in the device 10 when it is operational. The dashed line 14C depicts the long-axis or centerline of the fins 14. The portions of the fins 14 covered by the gate structure 16 are the channel regions of the FinFET device 10. In a conventional process flow, the portions of the fins 14 that are positioned outside of the spacers 18, i.e., in the source/drain regions of the device 10, may be increased in size or even merged together (a situation not shown in FIG. 1A) by performing one or more epitaxial growth processes. The process of increasing the size of or merging the fins 14 in the source/drain regions of the device 10 is performed to reduce the resistance of source/drain regions and/or make it easier to establish electrical contact to the source/drain regions. Even if an epi “merge” process is not performed, an epi growth process will typically be performed on the fins 14 to increase their physical size.
In the FinFET device 10, the gate structure 16 may enclose both sides and the upper surface of all or a portion of the fins 14 to form a tri-gate structure so as to use a channel having a three-dimensional structure instead of a planar structure. In some cases, an insulating cap layer (not shown), e.g., silicon nitride, is positioned at the top of the fins 14 and the FinFET device 10 only has a dual-gate structure (sidewalls only). Unlike a planar FET, in a FinFET device, a channel is formed perpendicular to a surface of the semiconducting substrate so as to reduce the physical size of the semiconductor device. Also, in a FinFET, the junction capacitance at the drain region of the device is greatly reduced, which tends to significantly reduce short channel effects. When an appropriate voltage is applied to the gate electrode of a FinFET device, the surfaces (and the inner portion near the surface) of the fins 14, i.e., the vertically oriented sidewalls and the top upper surface of the fin, form a surface inversion layer or a volume inversion layer that contributes to current conduction. In a FinFET device, the “channel-width” is estimated to be about two times (2x) the vertical fin-height of the fin 14 plus the width of the top surface of the fin 14, i.e., the fin width. Multiple fins can be formed in the same foot-print as that of a planar transistor device. Accordingly, for a given plot space (or foot-print), FinFET devices tend to be able to generate significantly higher drive current density than planar transistor devices. Additionally, the leakage current of FinFET devices after the device is turned “OFF” is significantly reduced as compared to the leakage current of planar FETs, due to the superior gate electrostatic control of the “fin” channel on FinFET devices. In short, the 3D structure of a FinFET device is a superior MOSFET structure as compared to that of a planar FET, especially in the 20 nm CMOS technology node and beyond. The gate structures 16 for such FinFET devices 10 may be manufactured using so-called “gate-first” or “replacement gate” (gate-last) manufacturing techniques.
For many early device technology generations, the gate structures of most transistor elements (planar and FinFET devices) were comprised of a plurality of silicon-based materials, such as a silicon dioxide and/or silicon oxynitride gate insulation layer, in combination with a polysilicon gate electrode. However, as the channel length of aggressively scaled transistor elements has become increasingly smaller, many newer generation devices employ gate structures that contain alternative materials in an effort to avoid the short channel effects which may be associated with the use of traditional silicon-based materials in reduced channel length transistors. For example, in some aggressively scaled transistor elements, which may have channel lengths on the order of approximately 10-32 nm or less, gate structures that include a so-called high-k dielectric gate insulation layer and one or more metal layers that function as the gate electrode (HK/MG) have been implemented. Such alternative gate structures have been shown to provide significantly enhanced operational characteristics over the heretofore more traditional silicon dioxide/polysilicon gate structure configurations.
Depending on the specific overall device requirements, several different high-k materials—i.e., materials having a dielectric constant, or k-value, of approximately 10 or greater—have been used with varying degrees of success for the gate insulation layer in an HK/MG gate structure. For example, in some transistor element designs, a high-k gate insulation layer may include tantalum oxide (Ta2O5), hafnium oxide (HfO2), zirconium oxide (ZrO2), titanium oxide (TiO2), aluminum oxide (Al2O3), hafnium silicates (HfSiOx) and the like. Furthermore, one or more non-polysilicon metal gate electrode materials—i.e., a metal gate stack—may be used in HK/MG configurations so as to control the work function of the transistor. These metal gate electrode materials may include, for example, one or more layers of titanium (Ti), titanium nitride (TiN), titanium-aluminum (TiAl), titanium-aluminum-carbon (TiALC), aluminum (Al), aluminum nitride (AlN), tantalum (Ta), tantalum nitride (TaN), tantalum carbide (TaC), tantalum carbonitride (TaCN), tantalum silicon nitride (TaSiN), tantalum silicide (TaSi) and the like.
One well-known processing method that has been used for forming a transistor with a high-k/metal gate structure is the so-called “gate last” or “replacement gate” technique. The replacement gate process may be used when forming planar devices or 3D devices. FIGS. 1B-1F simplistically depict one illustrative prior art method for forming an HK/MG replacement gate structure using a replacement gate technique on a planar transistor device. As shown in FIG. 1B, the process includes the formation of a basic transistor structure above a semiconducting substrate 12 in an active area defined by a shallow trench isolation structure 13. At the point of fabrication depicted in FIG. 1B, the device 10 includes a sacrificial gate insulation layer 19, a dummy or sacrificial gate electrode 15, sidewall spacers 16, a layer of insulating material 17 and source/drain regions 18 formed in the substrate 12. The various components and structures of the device 10 may be formed using a variety of different materials and by performing a variety of known techniques. For example, the sacrificial gate insulation layer 19 may be comprised of silicon dioxide, the sacrificial gate electrode 15 may be comprised of polysilicon, the sidewall spacers 16 may be comprised of silicon nitride and the layer of insulating material 17 may be comprised of silicon dioxide. The source/drain regions 18 may be comprised of implanted dopant materials (N-type dopants for NMOS devices and P-type dopants for PMOS devices) that are implanted into the substrate 12 using known masking and ion implantation techniques. Of course, those skilled in the art will recognize that there are other features of the transistor 10 that are not depicted in the drawings for purposes of clarity. For example, so-called halo implant regions are not depicted in the drawings, as well as various layers or regions of silicon/germanium that are typically found in high performance PMOS transistors. At the point of fabrication depicted in FIG. 1B, the various structures of the device 10 have been formed and a chemical mechanical polishing (CMP) process has been performed to remove any materials above the sacrificial gate electrode 15 (such as a protective cap layer (not shown) comprised of silicon nitride) so that at least the sacrificial gate electrode 15 may be removed.
As shown in FIG. 1C, one or more etching processes are performed to remove the sacrificial gate electrode 15 and the sacrificial gate insulation layer 19 to thereby define a replacement gate cavity 20 where a replacement gate structure will subsequently be formed. Typically, the sacrificial gate insulation layer 19 is removed as part of the replacement gate technique, as depicted herein. However, the sacrificial gate insulation layer 19 may not be removed in all applications. Even in cases where the sacrificial gate insulation layer 19 is intentionally removed, there will typically be a very thin native oxide layer (not shown) that forms on the substrate 12 within the gate cavity 20.
Next, as shown in FIG. 1D, various layers of material that will constitute a replacement gate structure 30 are formed in the gate cavity 20. The materials used for the replacement gate structures 30 for NMOS and PMOS devices are typically different. For example, the replacement gate structure 30 for an NMOS device may be comprised of a high-k gate insulation layer 30A, such as hafnium oxide, having a thickness of approximately 2 nm, a first metal layer 30B (e.g., a layer of titanium nitride with a thickness of about 1-2 nm), a second metal layer 30C—a so-called work function adjusting metal layer for the NMOS device—(e.g., a layer of titanium-aluminum or titanium-aluminum-carbon with a thickness of about 5 nm), a third metal layer 30D (e.g., a layer of titanium nitride with a thickness of about 1-2 nm) and a bulk metal layer 30E, such as aluminum or tungsten.
Ultimately, as shown in FIG. 1E, one or more CMP processes are performed to remove excess portions of the gate insulation layer 30A, the first metal layer 30B, the second metal layer 30C, the third metal layer 30D and the bulk metal layer 30E positioned outside of the gate cavity 20 to thereby define the replacement gate structure 30 for an illustrative NMOS device. Typically, the replacement gate structure 30 for a PMOS device does not include as many metal layers as does an NMOS device. For example, the gate structure 30 for a PMOS device may only include the high-k gate insulation layer 30A, a single layer of titanium nitride—the work function adjusting metal for the PMOS device—having a thickness of about 3-4 nm, and the bulk metal layer 30E.
FIG. 1F depicts the device 10 after several process operations were performed. First, one or more etching processes were performed to remove upper portions of the various materials within the cavity 20 so as to form a recess within the gate cavity 20. Then, a gate cap layer 31 was formed in the recess above the recessed gate materials. The gate cap layer 31 is typically comprised of silicon nitride and it may be formed by depositing a layer of gate cap material so as to over-fill the recess formed in the gate cavity and, thereafter, performing a CMP process to remove excess portions of the gate cap material layer positioned above the surface of the layer of insulating material 17. The gate cap layer 31 is formed so as to protect the underlying gate materials during subsequent processing operations.
Device manufacturers are under constant pressure to produce integrated circuit products with increased performance and lower production costs relative to previous device generations. Thus, device designers spend a great amount of time and effort to maximize device performance while seeking ways to reduce manufacturing costs and improve manufacturing reliability. As it relates to 3D devices, device designers have spent many years and employed a variety of techniques in an effort to improve the performance capability and reliability of such devices. Device designers are currently investigating using alternative semiconductor materials, such as so-called III-V materials, to manufacture FinFET devices, which are intended to enhance the performance capabilities of such devices, e.g., to enable low-voltage operation. For example, one prior art technique involved performing an epitaxial deposition process to blanket-deposit a III-V material on a silicon semiconducting substrate and thereafter performing an etching process to define the fins. Other prior art techniques involved utilization of selective epitaxial growth in trench/line structures formed on an otherwise planar surface. However, these methods have not achieved widespread adoption due to a variety of reasons. What is desired is a reliable and repeatable methodology for forming fins for FinFET devices that are comprised of an alternative material to that of the substrate. However, the integration of such alternative materials on silicon substrates (the dominant substrates used in the industry) is a non-trivial matter due to, among other issues, the large difference in lattice constants between such materials and silicon.
The present disclosure is directed to various methods of forming alternative channel semiconductor materials on a non-planar semiconductor device and the resulting device structure that may solve or reduce one or more of the problems identified above.